The present invention relates to an optical pickup for writing or reading information in or from an optical information recording medium, and more particularly to an optical pickup which uses a waveguide having a substrate made of Ti-LiNbO.sub.3, Si or the like and is suitable for fast accessing to an optical recording medium such as an optical disk, an optical card or the like.
The optical disks are widely used as compact disks for sound, video disks for image and memory disks for computers. To reduce the sizes of various apparatuses using the optical disks and to enable fast accessing to the optical disk, it is an indispensable requirement to reduce the size of an optical pickup for retrieving information from the optical disk and to remove a mechanical light deflector for attainment of fast accessing. However, any further reduction of the size of a lens and the further size reduction and speed-up of an optical light deflector driven by an electromagnetic coil are difficult. In order to solve this problem, studies of integration of optical elements on a single crystal plate in a thin film form have been conducted. According to Optoelectronics Conference `86 Technical Digest, pp. 64-65 (sponsored by The Institute of Electronics and Communication Engineers of Japan on 1986), a lens, a light detector and a grating for detecting auto-focus and tracking control signals are integrated on an Si crystal plate and a laser is disposed in proximity and stuck on to the Si crystal plate with a distance of 25 .mu.m maintained therebetween. Further, there is a try to integrate the laser itself on a waveguide substrate. However, this try has not yet been realized since there is a technique of matching Si or Ti-LiNbO.sub.3 with the waveguide substrate.
An optical pickup using a waveguide has been proposed by, for example, U.S. Ser. No. 842,200 filed on Mar. 21, 1986 and U.S. Ser. No. 151,964 filed on Feb. 3, 1988. In these proposals, no consideration is paid to introduction of a laser light into the waveguide at a high efficiency as well as a laser noise resulting from optical feedback upon introduction of the laser light. Further, no consideration is paid to a change in wavelength of the laser light associated with a change in state (from a write-in state to a read-out state or from the read-out state to the write-in state) and a corresponding instantaneous change in direction of a light passed through a light deflector element using a surface acoustic wave (SAW). Therefore, there is a problem that a light spot on an optical recording medium instantaneously deviates from a desired track or address upon change of the state.